Three dimensional displays add a third dimension to the viewing experience by providing a viewer's eyes with different views of the scene being watched. A popular approach for representing three dimensional images is to use one or more two dimensional (2D) images plus a depth representation providing information of the third dimension. Such an approach provides a number of advantages including allowing three dimensional views to be generated with relatively low complexity and providing an efficient data representation thereby reducing e.g. storage and communication resource requirements for three dimensional (3D) image (and video) signals. The approach also allows 2D images to be generated with different viewpoints and viewing angles than the 2D images that are included in the 3D image data.
A drawback of representing a 3D image by a single 2D image and associated depth information is that it does not include information about background image areas that are occluded by foreground objects. Accordingly, if the scene is rendered for a different viewpoint, no information can be revealed behind the foreground objects. Accordingly, it has been proposed to use multi-layer image and depth representations comprising a plurality of two dimensional images (e.g. a foreground image and a background image) with associated depth information. A description of how to render new views from such information can be found in Steven J. Gortler and Li-wei He, Rendering Layered Depth Images, Microsoft Technical Report MSTR-TR-97-09, a.o. available at http://research.microsoft.com/research/pubs/view.aspx?type=Technical%20Report&id=20 and in for example U.S. Patent Application US20070057944.
In approaches using more than one layer (i.e. a plurality of overlaying 2D images) it has been proposed to allow layers to be semi-transparent. In the field of computer graphics, such an approach is for example described in Norman P. Jouppi and Chun-Fa Chang, “An Economical Hardware Technique for High-Quality Antialiasing and Transparency”, Proceedings of Eurographics/Siggraph workshop on graphics hardware 1999. Such an approach allows semi-transparent materials to be visualised (e.g. water, smoke, flames) and also allows improved anti-aliasing of edges of objects at different depths. Specifically, it allows for a more gradual transition of edges. Thus, the transparency may not just be used for representing semi-transparent objects, but may also allow anti-aliasing of the edges of the foreground objects by making an edge semi-transparent such that a transparency value represents how much of a pixel should be foreground and how much of the background should visible. An example of such an approach can be found in: C. Lawrence Zitnick Sing Bing Kang Matthew Uyttendaele Simon Winder Richard Szeliski, “High-quality video view interpolation using a layered representation”, in Proceedings of Siggraph 2004.
However, a problem with such approaches is that backwards compatibility is suboptimal. In particular, in order to generate a 2D image, the 3D image data must be processed by an algorithm capable of understanding the three dimensional format. Accordingly, the signal cannot be used in traditional systems that do not have such functionality.
Also, another disadvantage of the approach is that it may in some scenarios not provide an optimal image quality. In particular, in some embodiments, the processing of the images and associated depth and transparency information will result in the rendered edges of foreground image objects being distorted.
Hence, an improved approach for 3D image data processing would be advantageous and in particular an approach allowing increased flexibility, improved backwards compatibility, improved image quality, facilitated implementation and/or improved performance would be advantageous.